Tuning the surface potential of Ag surfaces by chemisorption of oppositely-oriented thiolated carborane dipoles

Abstract

Two selected carboranethiol isomers were used to modify flat silver surfaces. Both isomers, 1,2-(HS) 2–1,2-C 2B 10H 10 (a) and 9,12-(HS) 2–1,2-C 2B 10H 10 (b), are relatively strong dipoles with two SH groups per molecule. They are both anchored to the surface via two SH groups per molecule. Topography and surface potential changes of the modified silver surfaces were studied using Scanning Kelvin Probe Force Microscopy (SKPFM). These measurements proved that both isomers are oppositely oriented on the surface. The former isomer increases, and the latter one decreases the surface potential of a modified silver film. The relative changes of the surface potential correlate well with the dipole moments of the isomers. Competitive chemisorption from a 1:1 mixture of both isomers shows that the isomer (a) is found in a significantly higher concentration on the surface than the isomer (b). This has been proved by both SKPFM and X-ray photoelectron spectroscopy (XPS) techniques. Additionally, contact angle measurements were carried out to characterise the modified surfaces, and these and XPS results show the presence of hydrophobic hydrocarbon contaminants.